Electrical device for determining the resistance or conductivity of bodies.



Patented Ian. I, IQOI.

ND. 664,9l5.

H. E. WARREN.

ELECTRICAL DEV'IGE FOR DETERMINING THE RESISTANCE 0B CDNDUCTIVITY 0F BODIES.

A iicauon' filed. Ian. 27, 1896.-

(Im Mariel.)

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rrun STATES PATENT OFFICE.

HENRY E. WARREN, OF NEWTON, MASSACHUSETTS.

ELECTRICAL DEVICE FOR DETERMINING THE RESISTANCE OR CONDUCTIVITY OF BODIES.

SPECIFICATION forming part of Letters Patent No. 664,915, dated January 1, 1901.

Application filed January 27, 1896. Serial No- 5'76,994=- (N0 model.)

To aZZ whom it may concern:

Be it known that l, HENRY E. WARREN, of Newton, in the county of Middlesex and State of Massachusetts, have invented certain new and useful Improvements in Electrical Devices for Determining the Resistance or Gonductivity of Bodies, of which the following is a specification.

This invention relates to a new and useful improvement in devices for determining the resistance or conductivity of bodies; and it consists in the novel features of construction and relative arrangement of parts hereinafter fully described in the specification, clearly illustrated in the drawings, and particularly pointed out in the claims.

Reference is to be had to the accompanying sheet of drawings, forming a part of this application, in which like characters indicate like parts wherever they occur.

Figure 1 represents a diagrammatic view of a device constructed in accordance with my invention. Fig. 2 represents a side elevation of the disk and the parts carried thereby. Fig. 3 represents a detailed View of the hammer h".

This invention has in View an instrument for determining the resistance or conductivity of bodies. While the galvanometer, if desired, may be used as a part of my instrument, I prefer to dispense with it, the latter requiring too much delicacy of adjustment for practical use by the ordinary Workman and by reason of its construction being unsuitable for the usage and handling to which instruments of this sort are subjected. The several parts of my invention can be mounted upon any suitable bed-plate, (not shown,) which forms no part of my invention.

a represents a dial-plate provided upon its rim with suitable decimal graduations a,preferably consisting of decimal parts of ohms. This dial-plate may be formed as a part of the bed-plate or may be secured thereto in any desired way. a represents a post rotatably mounted in the center of said dial-plate and carrying at one end a button a by which the said post and parts carried thereby may be turned. a represents a pointer secured to said post and having its free end arranged in the usual way over the decimal graduations at on the dial.

0. represents a disk of insulating material loosely mounted upon the post a and secured to the dial-plate a by a hub a or in any other desired way. This disk is provided upon its periphery with a groove a in which is arranged a wire a The ends of this wire are connected, respectively, to the binding-post 0L and to a metal bar 1), hereinafter described.

a represents an arm of conducting material rigidly mounted upon the post a and carrying at its end a spring-piece a arranged to press against the periphery of the disk a and make contact with the wire a The pointer a and the arm a being both rigidly connected to the post a are therefore always at a constant angular distance apart.

y, y','y and g represent standard coils, preferably having values in geometrical proportion of the ratio 10. These coils are connected at one end to a plate b and at their other ends each to a separate plate, (represen ted by the symbols b These latter plates 12 are arranged in close proximity to the plate I), each of said plates 1) and plate I) being formed with complemental depressions adapted to receive a metal plug b in order to close the circuit through any desired coil. The plug and the particular arrangement of the plates may be varied in any desired way, the essential being the arrangement of the resistance-coils.

6 represents a binding-post connected to the plate I).

03 represents a body, here shown as a Wire, whose resistance or conductivity it is desired to determine, connected at one end to a binding-post b of the plate 19 and at its other end to a binding-post a.

f represents a battery connected by a wire f to the binding-post a and by a wire f to the plate I). In this wire the ordinary contact-key f may be placed in order to shut off the current from the battery when the instrument is not in use.

f represents a shunt-wire leading from the wire f to the armature f of the electromagnet f.

f represents a wire leading tromagnet f to the plate b.

f represents a wire connecting the electromagnet f with a contact-screw f arranged to engage a spring) on the armature f h represents a telephone connected by a from the elec- Wire 7?. to the binding-post H carrying an anvil 7t it represents a wire connecting the telephone to the spring 72 mounted upon the post a and hearing at its center against the arm a.

frepresents what may be termed a current-detector device, whereby the presence or absence of a current in the line may be determined by the ear alone or preferably the use of the telephone. This detector in practice should be inclosed in a sound-proof box, so that its operations can be ascertained only by means of the telephone, and thus prevent confusion with outside noises. In this detector device f represents an electromagnet provided with an armature f to which are respectively connected wires f and J, as before stated.

71 represents a bar connected to the free end of the armature f in any desired way.

71 represents a hammer of conducting material secured at the free end of the bar h, but insulated therefrom.

- 72 represents an anvil of conducting material arranged to be engaged with the hammer h.

7L7 represents a light flexible wire connecting the hammer with the binding-post 72 to which is also connected the Wire h ,-leading from the plate I). The hammer is preferably arranged so that it will strike a sliding blow on the anvil in order to keep bright the points of contact between the two parts.

The detectorfis here shown as arranged to v be operated by a shunt from the circuitf;

but manifestly it may be operated bya separate battery or in any desired way. This detector in the form shown may be operated as a current-interrupter or as a current-varying device, depending upon the particular adjustment of the screw f whose purpose it is to limit the amplitude of vibrations of the armature. When the screw is in the position of adjustment shown in Fig. 1, the hammer is free to vibrate and move clear from all contact with the anvil. In this arrangement the device acts as a make-and-break or currentinterrupter. This interruption of the current in the telephone circuit will cause noises to be heard in the latter whenever and so long as any current tends to flow through the circuit. When the screw f is adjusted so as to engage the spring f suificiently to maintain the hammer continuously in engagement with the anvil, the detector will then act as a current-clearing device. In this arrangement the hammer will be maintained in close and continuous contact with the anvil during the vibration of the armature. There will, however, be variations of pressure between the hammer and the anvil as long as there is any current in the circuit,- and these variations of pressure will vary the resistance at the contact, as in the microphone. The variations in resistance will be different functions from the pressure variations according to the material composing the hammer and anvil. These variations in resistance in the circuit of the telephone will cause noises to be heard in the latter if any current is tending to flow through it, as when the current is interrupted in the arrangement of parts before referred to, so that the same result is accomplished by either arrangement. Either arrangement acts to operate the telephone when or while and so long as any current passes or tends to pass through the circuit.

The operation of the instrument just described is as follows: Any conductor 00 whose resistance it is desired to determine is introduced between the posts 19 and a", the telephone h is held to the ear, and the battery is thrown into circuit by means of the keyf.

Immediately the detector device is set in motion, and the hammer k strikes rapidly against the anvil 71. each time making and breaking the telephone-circuit, or when the hammer is maintained in contact with the anvil producing variations of pressure, which will alter the resistance at the contactand This point k V by means of the ordinary Wheatstone bridge,

that 2% equals When m is the resistance of the slide-wire from k to a n the resistance from 79 to b, y the known resistance for switching in by the plug 17 manifestly k is the function of 00. If y remains constant, the position of is (indicated by the pointer on the decimal graduations a) may be made a direct measure of m. From the equation it follows that if both y and a; are multiplied.

by any constantas, for instance, the ratio 10the ratio of m to 'n, and consequently the position of 70, will remain constant. Therefore exactly the same scale will serve for measuring values of a: separated by the ratio 10 with the simple change of the plug b and the decimal arrangement of the scale-reading a.

If desired, other ratios could be employed. 7

I have selected the ratio of ten by reason of its correspondence with the decimal system of notation.

Having thus explained the nature of my in- 7 vention and described a way of constructing and using the same, though without attempting to set forth all the forms in Which it may be made or all the modes of its use, what I claim, and desire to secure by Letters Patent,

1. A Wheatstone bridge comprising an arm having variable resistances, whose values are arranged in geometrical proportion having a ratio of ten, an arm formed by the resistance to be measured, a slide-Wire forming the other two arms, arranged in a circular path, a movable contact arranged to engage said wire to balance said bridge, a pointer controlled by said contact, a scale so graduated that said pointer, when said bridge is balanced, shall indicate on said scale a decimal part of the unknown resistance, a telephone in circuit with said bridge, and a current-detector device in said telephone-circuit, substantially as and for the purpose set forth.

2. A Wheatstone bridge comprising an arm having variable resistances, whose values are arranged in geometrical 'proportion having a ratio of ten, an arm formed by the resistance to be measured, a slide-Wire formingthe other two arms, arranged in a circular path, a movable contact arranged to engage said Wire to balance said bridge, a pointer controlled by said contact, a scale so graduated that said pointer, when said bridge is balanced, shall indicate on said scale a decimal part of the unknown resistance, a telephone in circuit with said bridge, and an electrically-operated current-detector device in said telephone-circuit, substantially as and for the purpose set forth.

3. A Wheatstone bridge comprising an arm having variable resistances whose values are arranged in geometrical proportion, an arm formed by the resistance to be measured, a slide-wire forming the other two arms, arranged in a circular path, a contact arranged to engage said wire to balance the bridge, a pointer controlled by said contact, a scale so graduated that said pointer, when said bridge is balanced, shall indicate on said scale a decimal part of the unknown resistance, a telephone in circuit with said bridge, a vibrating arm carrying a part arranged in the telephone-circuit, said part being controlled by the current in said circuit, and arranged to indicate in the telephone the presence or absence of the current in said circuit.

In testimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses, this 20th day of January, A. D. 1896.

HENRY E. WARREN.

Witnesses:

A. D. HARRISON, A. D. ADAMS. 

